This invention relates in general to gas detection and especially to gas detection in electron tubes. More particulatly, this inv ention relates to electro-chemical sensors which can measure the presence of gases in electron tubes and determine changes in the work function or electron emission capability in electron tubes due to gas contamination.
The contamination of the electron emitters by residual gases or the outgassing of absorbed or occluded constitutents is a serious problem in vacuum tubes. In particular, tube gases may build up while a tube is in storage and the resultant poisoning of the electron emitter by these gases is a major cause of tube failure during turn-on. Very low concentrations of some of these tube gases will change the work function of the electron emitter causing the tube to fail, while much larger concentrations of other gases will not significantly degrade a tube's performance. Therefore, it is desirable to monitor the build-up of various tube gases in vacuum tubes and to obtain information as to the type and concentration of these gases.
In the past, ordinary chemical gas-sensing techniques that utilize changes in visual appearance (e.g., the color change of getter flash or litmus-type indicators) have been employed. These are usually ineffective in sensing the low concentrations of gases that can change an emitter's work function and do not distinguish between types of gases. Gas analysers or ion gauges have been used to monitor tube gases, but these devices, in addition to being large, complex, and expensive, may not have the required sensitivity or distinguish between harmful and harmless gases. Actual work function measurements may be taken using the tube's cathode or an auxiliary cathode; however, this requires heating the cathode to thermionic temperatures or may involve turning the entire tube on. These latter techniques also alter the true gas content of the tube by ion-pumping and by generating additional gases.